Conventionally, as shown in FIG. 10, underfill 4, a material with a high elastic coefficient, has been filled between a semiconductor chip 2 and an organic substrate 1 in a Ball Grid Array (BGA) module 3 designed for mounting a flip-chip-type semiconductor chip 2 on the organic substrate 1. Such modules are typically referred to in the art as electronic packages. Since the thermal expansion coefficient of the semiconductor chip 2 is not the same as that of the organic substrate 1, the semiconductor chip 1 and the organic substrate 2, between which underfill 4 is sandwiched, are thermally expanded or shrunk independently under a change in temperature.
Accordingly, the behavior of these structures differs according to thermal coefficients of expansion of the semiconductor chip 2 and the substrate 1. For example, as shown in the much exaggerated view in FIG. 11, the module 3 may be deformed because of a rise or drop in temperature. Consequently, a BGA solder joint of the assembled module 3 may break, such that faulty connections are generated, thus exerting an adverse effect on the product's reliability. For this reason, the development of an electronic package which is not as affected by a change in temperature is strongly desired.
Laid-Open Japanese Patent Publication No. 62-249429 describes a semiconductor package in which a semiconductor "pellet" is bonded to a substrate and capped by metal or ceramics. In this package, in order to improve the radiation of heat generated inside the semiconductor "pellet", heat transfer from the semiconductor "pellet" to the cap is increased by putting the upper surface of the semiconductor "pellet" into contact with the inner surface of the cap, or through the medium of a space-filled metal. However, this publication does not mention a poor bonding between a substrate and a semiconductor chip, which is generated by warpage or deformation of the substrate caused by the difference in thermal expansion coefficient between the substrate and the semiconductor chip.